Atoms, Bonding, and Chemical Reactions Chapter 4 Sections 1, 2, and 3

Matter is anything that occupies space and has mass. Matter is composed of one or more elements. An element is a pure substance that cannot be broken down by chemical means. An atom is the smallest possible particle of an element.

Elements of Life There are 25 elements essential to life Trace elements make up less than.01% of your total body mass, but are essential for your health

Atomic Structure Atomic ParticleLocation in AtomCharge PROTONNucleusPositive NEUTRONNucleusNeutral ELECTRON In clouds outside nucleus Negative

Atoms and Isotopes In a neutral atom, the number of protons and electrons are equal The number of protons identifies the atom and is equal to the atomic number Isotopes have the same number of protons, but a different number of neutrons, and therefore have a different mass number Mass Number = # protons + # neutrons Some isotopes are radioactive, which means they decay over time, giving off radiation in the form of matter and energy

Electrons and Reactivity Electrons differ in the amount of energy they have, and how tightly they are held to the positive nucleus Electrons are assigned energy levels, and the number of electrons in the highest level determine how the atom will react (or bond) The group number on the periodic table determines the number of valence electrons

Practice/Review Atomic Number Number of Protons Number of Neutrons Number of Electrons Number of Valence Electrons 12 C C N O P S16 6 Atomic Number Number of Protons Number of Neutrons Number of Electrons Number of Valence Electrons 12 C6 14 C 14 N7 16 O8 30 P15 32 S16

Bonding In an effort to obtain full set of valence electrons, atoms will transfer or share electrons with other atoms This process creates an attraction (a chemical bond) that holds the atoms together The bond itself IS chemical energy! Compounds form when atoms of different elements combine in definite proportions

Ionic verses Covalent Bonds Ionic Bonding When one atom transfers electrons to another atom Strongest Bond Metal and Nonmetals Atoms that have gained or lost electrons become electrically charged and are called IONS (Ex: Na +, Ca 2+, Cl - )

Ionic verses Covalent Bonds Covalent Bonding When atoms share electrons Between Nonmetals Number of bonds is usually equal to the number of electrons the atoms needs to fill its valence shell Two or more atoms held together by covalent bonds form a MOLECULE (Ex: H 2 O, O 2 )

Other Bonds Polar Covalent Occur when electrons are shared unevenly between atoms Hydrogen Bonds Occur when a hydrogen atom in one molecule is attracted to a negative atom in another molecule

Van der Waals Forces Intermolecular forces of attraction between polar molecules Allow geckos to walk vertically on glass!!

Chemical Reactions Occur in a manner that conserves both matter and energy Starting materials are called REACTANTS Ending materials are called PRODUCTS